Mechanical Comprehension for ASVAB and PCAT

Introduction

• The video covers 21 practice test questions for the ASVAB and PCAT mechanical comprehension subtest.
• Important to practice without calculators or reference sheets, as they are not allowed in the actual test.
• Recommended to only spend a day or two preparing for this subtest.
• Everything needed is available freely on the YouTube channel.

General Advice

• Do not spend more than $30 on test prep for the ASVAB.
• If someone charges more, especially with a foreign accent, it may be a scam.

Topics Covered in Practice Questions

Lever and Mechanical Advantage

• Concept: Mechanical advantage (MA) of a lever is calculated as the distance from the effort to the fulcrum divided by the distance from the load to the fulcrum.
• Example: Pliers with a fulcrum at 6 inches from the effort and 2 inches from the load have an MA of 3.

Motion and Velocity

• Newton's First Law: Objects remain at rest or in uniform motion unless acted upon by an external force.
• Velocity Formula: Final velocity (V(t)) = Initial velocity (V(0)) + Acceleration * Time.
• Example: An object on a frictionless plane remains at its velocity if no external force acts on it.*

Gear Ratios

• Concept: Gear ratio affects rotational speed. A larger gear rotates more slowly than a smaller gear.
• Example: A gear with a 2:1 ratio spins twice as fast as its counterpart.

Pressure and Force

• Formula: Pressure = Force / Area.
• Example: 100 lbs of force over 2 sq in gives 50 psi.

Pulleys and Torque

• Torque Formula: Torque (T) = Radius (R) * Force (F).
• Example: For a 50 ft-lb torque with a 2 ft wrench, 25 lbs of force is needed.*

Fluid Mechanics and Piston Movement

• Pascal’s Law: Pressure is transmitted equally in all directions in a fluid.
• Surface Area Effect: Larger piston surface area moves less than smaller piston surface area.

Inclined Planes

• Force Calculation: Use weight and angle of incline to calculate force needed to prevent sliding.
• Example: Sine of the angle helps determine force using the formula: Force = Weight * sin(θ).*

Gearbox and Speed Calculation

• Method: Use gear ratios to calculate output speed from input speed.

Simple Gearbox Mechanics

• Rotational Direction: Mesh gears rotate in opposite directions.
• Speed Reduction: Larger gear (more teeth) rotates slower than smaller gear.

Balance and Lever Systems

• Formula: Force applied * Distance from fulcrum = Load weight * Distance to fulcrum.
• Application: Calculate the force needed to balance systems using this principle.

Conclusion

• Focus on understanding basic principles and formulas.
• Practice using mental calculations and understanding mechanical principles rather than memorizing complex formulas.